Five pieces, not five of something
A rack of shirts in size 40 is not a quantity in Nool. It is five rows, each with its own serial, each traceable to the bill it arrived on and — once it goes — the bill it left on.
Inventory
What is on the shelf, what moved, and what each supplier's month looked like.

A rack of shirts in size 40 is not a quantity in Nool. It is five rows, each with its own serial, each traceable to the bill it arrived on and — once it goes — the bill it left on.
Two tills scanning the same barcode cannot both succeed: whichever commits second is rejected. That is enforced in the database, inside the transaction that writes the sale, not by asking staff to be careful.
Filter by category, brand, model, colour or size and see what is on the shelf, what it is worth, what is not moving and what is running out.
Stock movement shows each piece's history — the purchase that brought it in, the sale that took it out, the return that brought it back.
Opening, purchases, sales and closing for one supplier, month by month: what was theirs on the 1st, what arrived, what sold, and what of theirs is still on your shelf.
Next module
Accounting →The quickest way to judge Nool is to watch a piece go from a supplier's bill to a printed tag to a bill at the counter. That takes about ten minutes.